brake controllers 'acting' differently in different vehicles

[Soundguy]

here's an odd one.

Ok.. I'm getting rid of my dodge 1500, I pulled the drawtight activator II out of it and just installed it into my f350 replacement truck I bought.

the dodge setup used one of those pigtails that plugs in under the dash, and you plug that into the controller. truck was already wired for a 7 pin plug, though I converted it to a 6 for my ag trailers. In that truck, pressing the brake or panic switch with no trailer hooked up just gave you a ' . ' on the controller. if you hooked up a trailer with brakes it gives you 0.0 untill you adjust up.. all the way to 10.. etc. on the f350, I again.. used a pigtail to plug in.. except.. the controller shows 0.0 when pressed ( even if adjusted up.. still shows 0.0 ).. if you hookup a trialer, you can then adjust up like normal. Road tests show the brakes work fine, and jacking trailer up to test shows no dragging. IE.. it works fine.. just reading odd when not hooked up to a trailer.

I even removed the polack 7 pin connector at the rear and cleaned it.. it wasn't dirty.. was shiney brass connectors.. even at the wire side. followe dhte harness to the plug in at the truck.. had nice clean 'greased' contacts. wire harness looks good.. there is a 4 pin there.. used a tester.. shows fine.

I ohmed out the power lines to the brake when unhooked.. no shorts to ground.. even used an analog meter.. weird...

as a test, I have a cheap HOPPY controller in my work truck. with no trailer it shows ERR, and with a trailer it shows5-100% in 5% increments. 5% is the lowest. Incedentally.. that work truck is a f250.

installing that hoppy to the 350 as a test.. it shows just like it does in the f250 ERR or 5-100% depending on if trailer hooked. brakes work fine. tested this on my 6 pin horse and flat bed trialer using the 6 to 7 converter i have ALWAYS used if I use my work truck or f450 to pull them as they are 7 pin. even tried my gooseneck which is 7 pin native and 2 brake axles vs the other single brake axles.

everything WORKS.. hoppy shows normal. drawtight shows odd.. but works.

might add I have a drawtight in my yukon as well.. and it displays like the dodge does. ' . ' when not hooked up.. 0.0-10 when hooked up.

weird? is this jhust a thing where the ford wireing 'looks' different to the controller or what?

all are installed in 98+ trucks using a pigtail to plug in under the dash. none had to be wired up manually using the brake sense line tap or anything. all vehicles were 'tow ready'. yukon I had to add a maxi fuse under the hood.. that's it.

coments?

either way it works.. just wondering...


soundguy

 

[ModMech]

Sound,

There are more ways to get trailer wiring wrong than right and I assume none of your tow vehicles were wired exactly the same.

Modern electronics can do strange things and when they do excessive resistance in the power or ground circuits is almost always the culprit. I would not use an ohm meter for anything other than PC board work, they physically cannot check how good a POWER or GROUND circuit works, but can only tell you there is a big problem or not.

Take a good headlamp and wire it up to a spare 6-way plug from brake + to B- and then re-try everything. You should get the same voltage at brake + for the same settings regardless of the vehicle the unit is installed in. If not, check the B+ connection UNDER LOAD with the brakes ON to the controller.

 

[Soundguy]

the issue is that the controller is acting differently when not loaded, and acts fine when loaded. ie.. the low resistance brake magnet circuit is not faulting.. it's only faulting at what I would consider a very high resistance.

I have seen brake circuits with excessive resistance in the brake line, and seen what it does. I have seent hem with the brake line shorted to ground.. again.. different issue.

am almost wondering if this drawtight is using a high freq PWM on the brake power out, and at that freq it's finding a 'signal' path to ground.. thouhg not one to carry current. IE.. a carbon track thru a wire.. or even a rust 'stain' across some plastic.. or a bit of cunductive corrosion at one of the dozens of connectors likely between the dash and bumper. something a 10k to 100k ohm input impeadance head might see as conductive to ground.. thouhg in practice carries no current, thus the brake controller never registers a % on the scale untill that low resistance brake magnet hits it's power and ground ..e tc. that's what my engineering background is telling me anyway..

soundguy

 

[Soundguy]

as a side note.. with magnets as cheap as they are.. I'm thinking of making up a test rig harness. I have the 4 pin tester for the turn signals, running and stop lamps. a mahnet looked from the brake power to ground, on a adapterized short harness and I'd have a good test harness. just pop in and go. I've made other testers liek that before.. could throw it all in a project box with an led readout and a stud out wire harness to plug in for 4-5-6-7 pin..

hmm.. winter project maybee..

 

[tcartwri]

FWIW the brake controller on our F550 never worked properly, until we bypassed the factory harness. We tried changing the controllers, went over the trailer wiring multiple times... had fights with the service manager.... etc..

Finally we brought the power and ground directly from the power block under the hood. Then all the errors went away and we had 5 times the braking force on the trailer.

Will your trailer stop your truck using the override? It should.

 

[ModMech]

That's why it is important to test circuits under LOAD, you should have B+ (+/- 0.5V) on a power circuit and B- (+/- 0.25V) on a ground circuit all while under load and relative to the negative terminal at the battery.

You will find 99% of your problems and even identify ones that were not yet apparent doing it this way.

 

[Soundguy]

Will your trailer stop your truck using the override? It should.

it will.

soundguy

 

[Soundguy]

hmm.. after the weekend I may try an unscientific test and remove the brake controll output wire from the molex on the controller, and run a long heavy gauge jumper to the back, and do the same on the 7pin, ie.. leave the brake output wire isolated completely end to end and see what I get.

I'm still thinking it is a HIGH impeadance reference to ground.. something one controller may see, but perhaps not others..

soundguy

 

[RobertN]

Can you explain that more?

I usually debug using Volt, Ohm, and also load circuits. An Ohm meter( good one) should be able to tell you if there is resistance in a line that would affect current flow under load. Volts under no load may tell you you have a connection, but does not reflect the IR losses and resistive components of the circuit.

A decent DVM will allow you to measure a fair amount of current too.

excessive resistance in the power or ground circuits is almost always the culprit. I would not use an ohm meter for anything other than PC board work, they physically cannot check how good a POWER or GROUND circuit works, but can only tell you there is a big problem or not.

 

[tlbuser]

Can you explain that more?

I usually debug using Volt, Ohm, and also load circuits. An Ohm meter( good one) should be able to tell you if there is resistance in a line that would affect current flow under load. Volts under no load may tell you you have a connection, but does not reflect the IR losses and resistive components of the circuit.

A decent DVM will allow you to measure a fair amount of current too.

IMO, either method, clamp-on or load will work. Direct load is more of an old school fail safe. You could use your battery load tester connected to the 7 pin plug instead of a headlamp and a couple of wires.